Engines are classified by cylinder arrangement form as in-line, V-shaped, and the like. The in-line engine has cylinders arranged in series. The V-shaped engine has cylinders positioned in a V-shape. In the V-shaped engine, side cylinder heads are placed on respective upper portions of a substantially V-shaped cylinder block, whereby side cylinder banks are arranged in a substantially V-shape.
The V-shaped engine is defined with a void or space between the side cylinder banks. The space has an intake manifold placed therein. The V-shaped engine is further provided with cooling water distribution pipes such as cooling water intake and exhaust pipes. In addition, a thermostat is disposed midway between these two different cooling water pipes. The intake pipe introduces cooling water from a radiator into a water pump. The water pump is disposed on one side of the engine at one axial end of a crankshaft. The cooling water is collected on the other side of the engine at the other axial end of the crankshaft after passing through the cylinder banks. The aforesaid exhaust pipe returns the collected cooling water to the radiator.
An example of a mounting position structure for the thermostat is disclosed in published Japanese Patent Application Laid-Open No. 62-199921. A cooling system for an engine as disclosed in this publication includes a radiator inlet passage, a radiator outlet passage, a bypassing passage, and a thermostat. The radiator inlet passage interconnects a cooling water outlet of the engine and a radiator inlet. The radiator outlet passage interconnects a radiator outlet and a water pump inlet. The bypassing passage is connected between both of the above passages. The thermostat is disposed where the bypassing passage and the radiator outlet passage are joined together. In the thermostat-mounting position structure, a body of a water pump is provided on a front end surface of a cylinder block at a transverse position thereof. In addition, a thermostat case, in which the thermostat is positioned, is mounted behind the water pump body. This arrangement is designed to attain a reduction in and compactness of the entire engine length.
Another example is disclosed in published Japanese Patent Application Laid-Open No. 4-276137. In the thermostat structure for an engine as disclosed in this publication, an intake manifold has branch pipes arranged in a plane non-perpendicular but slanted at a predetermined angle with respect to the axis of the crankshaft of the engine. This arrangement causes a surplus gap to emerge from the void or space. Then, a thermostat is disposed in the surplus gap. As a result, the thermostat is placed without projecting from the engine, thereby making it possible to overcome an inconvenience that would otherwise increase the size of the engine. Further, the engine can be disposed in an engine room without interfering with other components, thereby providing improved loading capability to vehicles.
Still another example is disclosed in published Japanese Utility Model Application Examined No. 5-17383. In a cooling system for an engine disclosed in this publication, a cylinder block is defined with a thermostat case, and a cooling water hose is connected at one end to a cover of the thermostat case. The cooling water hose is connected at the other end to a radiator. Before terminating at the radiator, the cooling water hose extends through a space between first and second auxiliary devices. The auxiliary devices are arranged one atop the other, while being located near and in front of an exhaust manifold. Furthermore, the auxiliary devices partially extend between the cooling water hose and the exhaust manifold so as to reduce the quantity of passive heat from the exhaust manifold, thereby alleviating thermal load. As a result, the cooling water hose is isolated from radiant heat from the exhaust manifold without the use of particular heat-insulating materials.
As illustrated in FIG. 5, in conventional thermostat-mounting position structures, a large-sized auxiliary device 118 such as an A/C compressor is usually disposed on an air exhaust side of the engine 102 at a lower portion thereof. In addition, a water pump 120 and a thermostat case portion 124 are positioned on the same exhaust side.
In this construction, center positions of first through fourth exhaust ports 112-1, 112-2, 112-3, and 112-4 are coincident with center position (#1, #2, #3, #4) of unillustrated cylinders of the engine 102. This configuration causes a volumetric reduction in a void space 122 that is defined between the water pump 120 and an exhaust manifold 114. As illustrated in FIG. 6, the result is that the thermostat case portion 124 must be protruded outwardly from the engine 102 when being placed in the void space 122.
Consequently, such arrangement of the thermostat case portion 124 results in increased width L1 of the engine 102, which leads to a large-sized engine. This causes an inconvenience in that it is disadvantageous to place such a large engine into vehicles whose engine rooms are limited in space availability. In addition, the thermostat case portion 124 is spaced apart from the rotational center of the engine 102, i.e., from the crankshaft 116. This spacing causes another inconvenience in that the thermostat case portion 124 has less resistance to vibration, which is disadvantageous in view of practical use.
FIG. 7 illustrates another known engine 202 in which a large-sized auxiliary device 218 is placed on an air outlet side of the engine 202 at an upper portion thereof. In this case, either a water pump 220 or a thermostat case portion 224 must be positioned side by side with a crank case (not shown) under the auxiliary device 218.
However, when the water pump 220 is positioned side by side with the crank case, a water jacket for cooling the water pump 220 is eliminated. Accordingly, the engine 202 requires piping for interconnecting the water pump 220 and the water jacket that is defined in a cylinder block. However, such requirement involves laborious fabrication and a complicated construction as well, thereby causing inconveniences of: increased cost, which is disadvantageous from an economical viewpoint; and, a dimensional increase in the engine.
Furthermore, an auxiliary component such as an oil filter and a retention component such as an engine-mounting bracket must be provided behind a position at which either the water pump of the thermostat case portion is disposed. This arrangement creates an inconvenience, which is disadvantageous in view of practical use, in that it is difficult to provide a bypassing pipe to a thermostat in the thermostat case portion.
In order to obviate the above-described inconveniences, the present invention provides a thermostat-mounting position structure for an engine having an exhaust manifold placed on an air outlet side of the engine and having an auxiliary device and a water pump both positioned on the air outlet side of the engine toward one axial end of the crankshaft, the auxiliary device and the water pump being situated respectively at lower and upper portions of the engine, the improvement wherein at least one of exhaust ports located on one side of the engine at one axial end of the crankshaft is moved offset toward the other axial end thereof, thereby forming a void space between the water pump and the exhaust manifold, and wherein a thermostat case portion for a thermostat is placed in the void space.
According to the present invention having the above structure, at least one of the exhaust ports is positioned offset toward the other side of the engine at the other axial end of the crankshaft, whereby the void space is caused to be formed between the water pump and the exhaust manifold. Further, the void space has the thermostat case portion for a thermostat disposed therein. This structure eliminates the likelihood that the thermostat case portion needlessly extends outwardly from the engine. Accordingly, a smaller-sized engine is achievable, which consequently improves the loading capability of vehicles. Furthermore, the thermostat is located adjacent to the rotational center of the engine, and the resistance of the thermostat to vibration is enhanced.